Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

20°C

5°C

2. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

None of these

Positive

3. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser

Condenser, absorber and separator (rectifier)

4. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

5. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

6. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Sub-cooling or under-cooling

Normal cooling

7. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

8. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

9: 1

1: 9

9. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

10. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

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11. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

12. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

13. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Relative humidity

Wet bulb temperature

14. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Ammonia

Freon

Brine

15. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.4

0.6

0.67

16. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

0.1 ton

5 tons

17. Freon group of refrigerants are

Inflammable

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

18. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

4.33

3.33

19. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

8 bar

30 bar

20. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

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21. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

22. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Ericson

Stirling

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

24. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

25. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-75.2°C

-56.6°C

26. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

27. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always more than unity

Always less than unity

28. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

29. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

Water will never evaporate

30. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

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31. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

32. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

33. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

Low

High

34. A thermostatic expansion valve in a refrigeration system

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

35. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Axial

Piston type reciprocating

36. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

37. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

38. The capillary tube, as an expansion device, is used in

All of these

Room air conditioners

Domestic refrigerators

Water coolers

39. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

40. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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